Early cable driven general purpose dental handpieces were subsequently replaced by belt and pulley driven straight handpieces that could accommodate long straight burrs or "contra-angle" attachments. The "contra-angle" attachments had a slight bend or angle at the junction of the shank and handle of the handpiece.
In all these early dental handpiece designs, the drill burr was arranged to exit the fixed head of the handpiece at a 90.degree. angle in relation to the handpiece shank. It is believed that this 90.degree. angle arrangement was the result of the use of intermeshing metal drive gears in the early, slower speed cable and belt driven handpieces. With the advent of the high-speed air-driven handpieces in the early 1950's, the fixed head dental handpiece continued to be manufactured with a burr axis oriented at a 90.degree. angle to the shank of the handpiece. It has been discovered that the 90.degree. exit angle for the burr from the fixed head of a general purpose dental handpiece is not an optimum angle for most routine dental procedures.
High-speed, air-driven dental handpieces are known which have the burr axis oriented in a fixed position at an angle other than 90.degree., e.g., 45.degree. or 135.degree., for special applications, such as, for example, surgical applications in some third molar procedures (impacted wisdom teeth) and the like. However, such handpieces are not suitable for general purpose tooth reduction and caries removal and most other routine dental procedures.
Dental handpieces with varying drive mechanisms are also known which have angularly articulatable heads so that the burr axis can be positioned at different selected angles relative to the handpiece shank. U.S. Pat. Nos. 623,469; 647,010; 1,039,420; 1,333,809; 1,379,880; 4,281,989; and 4,303,393 are representative of such articulated head dental handpieces, both in the lower speed dental handpieces as well as in the high-speed, air-driven dental handpieces. Such handpieces have a relatively complex design incorporating several drive gears or fluid flow paths and, because of their complexity and cost, are simply not used by most dentists.